What Causes Ice Dams and How Can You Prevent Them?

Looks can be deceiving. For instance, there are few things as lovely as icicles hanging from roof eaves and gutters. In some regions, they dangle for months, like crystal jewels, sparkling in the sunshine. And yet, in many cases, they signal that the roof may have a problem with ice dams that needs attention before water seeps into the house.

What causes ice dams on roofing?

Ice dams — literal dams made of ice — usually form at eaves and gutters and prevent snow- and ice-melt from leaving the roof. They’re often caused by a temperature imbalance in the attic. As heat rises in the house and makes its way into the attic, the upper portion of the roof may warm faster than the lower portion at the eaves. If the upper portion becomes warm enough to melt snow (above 32°F) while the lower portion remains below 32°F, snow will melt, flow down the roof, and refreeze before it can flow off the edge. This can also be compounded by naturally rising ambient temperatures during the day and falling temperatures at night. What results is a dam, which will hold the remaining water, snow, and ice on the roof.

There are two main causes of this kind of temperature imbalance:

•  Poor attic insulation. Insufficient or deteriorated attic insulation can allow warm air to move from the heated areas of the house to the attic space.
•  Lack of proper attic ventilation. Properly balanced attic ventilation helps slow snow melting by allowing cold air to enter the attic space, in turn driving out warmer air. This reduction in warm attic air helps decrease the chance of snow melting on the roof.

Why are ice dams a problem?

Almost all roofing materials are designed to shed water. As ice melts and refreezes, it can damage the shingles and other parts of the roof system. And when a growing ice dam pushes water back up the roof slope, that water may flow under the shingles and penetrate into the roof system or house below. That’s why GAF factory-certified roofers will always recommend a layer of strong protection like WeatherWatch® or StormGuard® Leak Barrier. These products help prevent leaks due to water backing up in your gutters, wind-driven rain, and, of course, damaging ice dams. They are self-adhering membranes that seal around fasteners and other protrusions in the roof, helping to protect the most vulnerable areas of your roof against leaks.

What can I do about ice dams?

Here are 3 steps you can take to prevent ice damming this winter:

1. Remove snow from the roof. Depending on the size and accessibility of your roof, you can use an extendable snow roof rake to (carefully) pull fresh snow off the roof before the melt-and-freeze cycle even begins. Snow and ice removal can be dangerous work and if done improperly you might risk injury to your shingles – or more importantly – yourself! We strongly encourage you to engage the services of a professional to assist with snow and ice removal. 
2. Ventilate. Ensure you have a properly-balanced attic ventilation system that allows fresh air to continuously move through the attic space under your roof. To find out how much ventilation you should have, use our ventilation calculator.
3. Insulate. Proper attic insulation will do more than prevent ice dams; it can also help reduce your heating costs by keeping warm air in your living space, where it belongs.

Contact Us

Contact us if you have any additional questions about what causes ice dams or if you need assistance with any roof installations.  We always offer free roof inspections with every visit. 

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